Forest biological firebreaks are considered an essential measure for preventing the spread of forest fires and protecting forest resources. By planting fire-resistant plants to create a fire barrier, the spread of fire can be effectively slowed. To study the impact of firebreak width on forest fire barriers, fire dynamics simulator software was used to construct symmetrical hillside terrain with varying slopes, and BlenderGIS was employed to obtain and simplify a typical forest field in the Lingnan region. Simulation tests were conducted by modifying the width of the firebreak at the top of the slope. The results indicate that, under symmetrical hillside terrain, a 9 m wide firebreak effectively blocks the spread of surface fires. However, for crown fires, the firebreak is effective in preventing spread on gentle slopes, while steep slopes still show the potential for fire propagation. In the actual terrain, a 3 m wide firebreak is found to be effective in preventing the spread of surface fires. For crown fires, due to the wider and gentler topography of the slopes, crown fires did not spread to the rear slopes, making it difficult to assess the impact of firebreaks on crown fires.